How attainable is Keystone Hero as a Ret paladin with no prior M+ experience?

I feel kind of silly for even asking this because I'm a solo player in a guild consisting purely of my own alts who primarily gears through running delves. I normally wouldn't care about this sort of thing but I would really like to get the "Void Wear Prohibited" achievement to put the Mythic glow intensity on the Normal shoulders from this tier's paladin set.

Based on the fact that the DF S1 equivalent achievement "Deep Cuts From the Vault" still exists, I suppose I could always get it via clearing Mythic Dimensius in the far future, but that would mean waiting until The Last Titan is out (if not even later), and I'd like to avoid that if possible.

Should I just wait until later in the season to pursue this, and just keep gearing up via T11 delves in the meantime? I don't even know what 2500 M+ rating means in terms of how to get it, I haven't pursued any kind of rated content since achieving 1800 in BG Blitz back in TWW S1.

EDIT: I am in NA region, forgot to mention that.